When an election ends, the question we most often ask is “why?” Did Barack Obama put together a “coalition of the ascendant”—newly powerful numbers of blacks, Hispanics, college-educated young? Did Donald Trump shock us by summoning an army of the left-behind, who carried economic insecurity and racial resentments to the polls?

But often, there’s another, much simpler answer: Just look at the rules.

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The “terms and conditions” of a political race may well matter more than any other factor. And if you really need a reminder of how crucial the rules of an election are to its outcome—how, for example, a candidate can win 3 million more votes than her opponent and lose—two current examples from across the Atlantic should make the case strikingly clear.

In France, with a presidential election being watched around the world for the chance a right-wing nationalist or a far-left populist could win, the only certain outcome of the vote Sunday is that there will be no winner: The top two finishers will meet in a decisive runoff two weeks later.

Then there’s Great Britain, which will have a general parliamentary election years earlier than expected—on June 7, to be exact—because Prime Minister Theresa May exercised her power to call a “snap” election. The entire campaign season will run about six weeks from start to finish—a length unimaginable here, where prospective 2020 presidential candidates are already checking flight schedules to Des Moines and Manchester.

Either one of those systems would lead to radically different outcomes in U.S. presidential elections—where a winner can (and often does) become president without a majority of the popular vote, and where the length of the campaign puts huge emphasis on finances, backing, media campaigns and pure stamina.

The French system is based on a simple premise: No one should lead the nation unless he or she commands an absolute majority of voters. If nobody achieves a majority in the first round, the two winners face off one-on-one. In the U.S., many of our elections—for mayor, governor, House and Senate seats—are held under the same standard. But our presidential campaigns aren’t: They require a majority of the Electoral College, which isn’t the same as the popular vote. While the champions of Al Gore and Hillary Clinton are painfully aware of the results this system can produce, the full story of how “absolute majority” voting would change American politics is nothing less than eye-opening.

Since 1960, no fewer than five presidents have been elected even though more total votes were cast against them than forthem: John F. Kennedy in 1960, Richard Nixon in 1968, Bill Clinton in 1992 and 1996, George W. Bush in 2000, and Trump in 2016.

Now imagine if we had a runoff in place, to assure that our presidents had popular majority backing. Who would have their portraits on the wall?

It’s highly likely that Al Gore would have won such a contest in 2000; the center/left candidates (Gore and Ralph Nader) outpolled the center/right candidates (Bush and Pat Buchanan) by some 3 million votes. It’s likely that Hillary Clinton, flawed as she was as a candidate, would have bested Trump in a runoff with voters who had chosen Gary Johnson and Jill Stein or who had stayed home the first time, but now realized that Trump might actually win.

Other alternate outcomes are foggier. Given the historic closeness of the 1960 popular vote—JFK had an official plurality of 0.1 percent—a Nixon victory in a runoff would have been at least plausible. There’s a persistent myth about the 1992 campaign that Ross Perot’s 19 percent of the popular vote cost George H.W. Bush the win, although exit polls then showed that Perot voters would have split evenly between Bush and Bill Clinton. So a Clinton victory in a runoff would have been the likely outcome. Even discounting for speculation, it’s still striking that a different system would have given us Nixon instead of Kennedy, Gore instead of Bush, and Hillary Clinton instead of Trump, and likely some very different history.

Now look across the ocean to Great Britain, and the prime minister’s call for a “snap” election. This concept is radically alien to us Americans, where fixed terms for office are more or less universal. In this case, May brushed aside her own promise not to go to the polls until 2020, arguing that she needed a clear mandate to proceed with the “Brexit” divorce from the European Union. Under a 2011 law, she no longer has the power to call an election unilaterally, as previous prime ministers did, but can still do so if two-thirds of the House of Commons approves, which in this case is a near-certainty.

Look at the advantage that snap elections give the government in power. Right now, the opposition Labour Party is hopelessly divided. A clear majority of MPs reject the party’s leader, Jeremy Corbyn, who remains in power because of the broader party membership. Instead of having almost four years to regroup, the party must scramble to compete in constituencies across the country with a huge deficit of finances and even candidates. Moreover, a system with no absolute fixed terms means a government can pick its own moment for reelection: It can watch for such weakness in an opposition, and announce: “OK, we're going to the polls in six weeks.” Or it could wait for a moment of singular success on its part. Imagine if George H.W. Bush had been able to order up an election six weeks after the triumphant end of Operation Desert Storm in 1991, with a Kuwait liberated and a U.S. standing proudly astride the world stage. (Instead, he tried to get re-elected in the teeth of the next year’s recession.) No wonder President Kennedy is said to have remarked that if he had the power to call snap elections, he could have remained in power more or less permanently.

These systems might sound strange to us, but then our own Electoral College system looks downright exotic, not to say mystifying, to most other democracies. If you measure these overseas examples against our system of nominating and electing presidents, you can see just how much the rules of the game matter. This even extends to primaries: Had the Republicans been operating by the Democratic Party’s rules—no winner-take-all contests, hundreds more unbound “superdelegates”—Trump’s path to the nomination would have been much harder. And if we allocated electoral votes by congressional district, the 2012 race would have been much closer; Mitt Romney won 226 districts to Obama’s 209.

It’s a lesson at the heart of politics, one as clear as it is overlooked in so much political analysis: the rules of the road are often the most critical factor in determining who wins. Presidents who trumpet their victories and claim a mandate should be careful what they’re claiming: Often it’s the rules, as much as the people, that put them there.